1. Field of the Invention
The present invention relates generally to a method for accessing optical fibers within a buffer tube and, in particular, relates to a tool and method for accessing optical fibers within a buffer tube.
2. Description of the Prior Art
The use of protective buffer tubes for packaging optical fibers is well known in the telecommunications industry. Buffer tubes protect the optical fibers from stress induced attenuation and physical damage. Although many different optical fiber cable configurations are known and used in the telecommunications industry, one of the more popular designs includes grouping a series of buffer tubes around a central strength member with the entire assembly being encased in an outer protective sheath. The outer protective sheath may be made from a variety of materials including steel, plastic or other suitable material. The interior of the protective sheath around and between the buffer tubes can be filled with a water resistant, lubricating material, such as filling compound or other water blocking material. The optical fibers are typically loosely laid in the buffer tubes and the loose space within the tubes filled with a gel to provide lubrication, water resistance and minimize the stress placed on the fibers.
In some optical fiber configurations, the buffer tubes are helically wound around the central strength member. Often, the helical lay may be in one direction for the entire length of cable. Alternatively, a reverse oscillating lay configuration can be used in which the winding direction periodically alternates between a left and right lay. For example, Alcatel Telecommunication Cable Inc. sells a reverse oscillating lay configuration optical fiber cable under the name Non-Armored Loose Tube Yarn Reinforced Optical Fiber Cable.
As with conventional electrical conducting cable, splices to optical fiber cables are inevitable for connecting multiple cable lengths to construct a route, repairing a fiber breakage, re-routing service or adding an intermediary device. Often, this may involve accessing optical fibers contained in a single buffer tube while leaving the remaining buffer tubes intact. Accessing optical fibers contained within a single buffer tube without compromising the integrity of other buffer tubes in the cable can be difficult. For example, helical lay cables typically do not provide much slack in the buffer tubes. Consequently, it can be difficult to pull a single buffer tube away from the cable to access it.
A reverse oscillating lay cable configuration provides easier access to a single buffer tube in a midsection of a cable length once a section of the outer protective sheath has been removed to expose at least one change in winding direction. The oscillating lay provides slack to pull a single buffer tube away from the other buffer tubes in the cable. Once a single buffer tube has been pulled away from the cable, is easier to gain access to the optical fibers contained within.
Notwithstanding the obvious advantages that a reverse oscillating lay cable configuration offers over other configurations, it is not without its own problems. Although the alternating lay configuration provides more slack when the outer sheath is removed, the buffer tubes tend to retain their original shape, even when pulled away from the cable. The result of this "oscillation history" is that the buffer tube retains sharp bends, particularly at the point where the lay direction changes. A bent or curved shaped buffer tube can be more difficult to access, particularly with a conventional optical fiber access tool having a narrow aperture for receiving the buffer tube. The high resistance created by the bends can make it difficult to pull the tool along the buffer tube, resulting in binding and possibly buffer tube breakage.
For example, U.S. Pat. No. 5,093,992, issued to Temple et al. on Mar. 10, 1992, discloses a tube slitting tool having a radially mounted cutting blade for slitting a tube along its length. The narrow buffer tube channel makes it unsuitable for use with helically wound or bent buffer tubes. Moreover, the radial cutting blade of Temple et al. is hidden from view from the user, which may result in a more intrusive cut than necessary, possibly damaging the underlying optical fibers.
U.S. Pat. No. 4,972,581, issued to McCollum et al. on Nov. 27, 1990, discloses a fiber access tool having a cutting blade mounted transversely to a buffer tube for removing a chord of buffer tube. Unlike the Temple et al. blade, the transversely mounted cutting blade of McCollum et al. is less intrusive and less likely to damage the underlying optical fibers. However, the buffer tube channel of McCollum et al. is narrow and has a uniform cross-sectional area throughout. Consequently, the McCollum et al. tool would not work well with a helically wound or bent buffer tube because the buffer tube would offer too much resistance, possibly binding with or breaking the buffer tube.
Consequently, a tool which provides access to optical fibers contained in a helically wound or reverse oscillating lay buffer tube with low pulling resistance, minimal intrusion into the tube and in open view of the user is highly desirable.